Note 1 - Nature of Business and Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2015

Accounting Policies [Abstract]

Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions [Table Text Block]

	2015			2014			2013
Dividend yield	.37%	to	.46%		.47%		.44%	to	.53%
Expected volatility	28.92%	to	29.32%	29.07%	to	29.18%	29.50%	to	30.56%
Risk-free interest rate	1.89%	to	2.37%	2.69%	to	2.82%	1.71%	to	2.90%
Expected life of option grants (years)		6			6			6
Weighted-average grant date fair value		$5.11			$5.68			$5.14

	2015			2014			2013
Dividend yield	.37%	to	.45%	.46%	to	.47%	.53%	to	.61%
Expected volatility	8.81%	to	13.10%	16.96%	to	19.35%	23.05%	to	24.25%
Risk-free interest rate	.09%	to	.16%	.04%	to	.12%	.10%	to	.18%
Expected life of purchase grants (months)	3	to	6	3	to	6	3	to	6
Weighted-average grant date fair value		$2.39			$2.37			$2.10